In recent years, techniques have been sought that enable the efficient production of monocyclic aromatic hydrocarbons of 6 to 8 carbon number (such as benzene, toluene, ethylbenzene and xylene, which are hereinafter jointly referred to as the “BTX fraction”), which can be used as high-octane gasoline base stocks or petrochemical feedstocks and offer significant added value, from feedstocks containing polycyclic aromatic hydrocarbons such as light cycle oil (hereinafter also referred to as LCO), which is a cracked light oil produced in a fluid catalytic cracking (hereinafter also referred to as FCC) that has conventionally been used as a diesel oil or heating oil fraction.
Examples of known methods for producing a BTX fraction from polycyclic aromatic hydrocarbons include the methods listed below.
(1) Methods of hydrocracking hydrocarbons containing polycyclic aromatic hydrocarbons in a single stage (see Patent Documents 1 and 2).
(2) Methods of subjecting hydrocarbons containing polycyclic aromatic hydrocarbons to a hydrotreatment in a preliminary stage and then hydrocracking in a subsequent stage (see Patent Documents 3 to 5).
(3) A method of converting hydrocarbons containing polycyclic aromatic hydrocarbons directly into a BTX fraction using a zeolite catalyst (see Patent Document 6).
(4) Methods of converting a mixture of hydrocarbons containing polycyclic aromatic hydrocarbons and light hydrocarbons of 2 to 8 carbon number into a BTX fraction using a zeolite catalyst (see Patent Documents 7 and 8).
However, the methods of (1) and (2) require the addition of high-pressure molecular hydrogen, and the high level of hydrogen consumption is also a problem. Further, under the hydrogenation conditions employed, an unnecessary LPG fraction tends to also be produced in a large amount during production of the target BTX fraction, and not only is energy required to separate this LPG fraction, but the feedstock efficiency also deteriorates.
The method of (3) was not entirely satisfactory in terms of conversion of the polycyclic aromatic hydrocarbons.
The methods of (4) have been designed to improve the thermal balance by combining a production technique for BTX that employs light hydrocarbons as a feedstock and a production technique for BTX that employs hydrocarbons containing polycyclic aromatic hydrocarbons as a feedstock, but have not been designed to improve the yield of BTX from the polycyclic aromatic fraction.